The present invention relates to improvements in color printing machines used to color print a running web of paper, and particularly to a color printing machine having a plurality of printing units each including a plate cylinder and an impression cylinder, and a web length adjusting unit located between each pair of adjacent printing units.
FIG. 1 shows a conventional color printing machine which has an impression cylinder 1 and plate cylinders 2 (as many as the printing colors) mounted in contact with the periphery of the impression cylinder. As the web 4 to be printed passes between the impression cylinder 1 and the plate cylinders 2, it is printed by plates 3 mounted on the plate cylinders so as to enclose their whole periphery. The impression cylinder and the plate cylinders are driven from a single motor through a geared transmission for synchronized printing. Since the diameter of the plate cylinders is determined by the printing length which is the length of the plate, each time the printing length changes, new plate cylinders having a peripheral length corresponding to the new printing length have to be manufactured. This increases the printing cost. Furthermore, each time the printing length changes, heavy plate cylinders have to be replaced with new ones. New plate cylinders with new plates mounted thereon have to be mounted on the impression cylinder with a suitable contact pressure. This is a very troublesome work. Furthermore, fine adjustment of the transmission gear was necessary for phase tuning between the plate cylinders for accurate registration. Another disadvantage is that a lot of plate cylinders have to be maintained.